ACTINOMYCETES These organisms have been shown to be higher bacteria, but they were thought to be fungi for many years because they have filamentous forms, 0.5 to 0.8 µ in diameter, which appear to branch.

Some species form aerial mycelia in culture. The clinical manifestations of infection are similar to those of a systemic fungal infection. It is now clear that they are not fungi but are closely related to the mycobacteria.

ACTINOMYCOSIS

The most common cause of actinomycosis is the organism Actinomyces israelii which infects both man and animals.

In cattle, the disease is called "lumpy jaw" because of the huge abscess formed in the angle of the jaw.

In man, A. israelii is an endogenous organism that can be isolated from the mouths of healthy people. Frequently, the infected patient has a tooth abscess or a tooth extraction and the endogenous organism becomes established in the traumatized tissue and causes a suppurative infection.

Appearance

These abscesses are not confined to the jaw and may also be found in the thoracic area and abdomen. The patient usually presents with a pus-draining lesion, so the pus will be the clinical material you send to the laboratory. This diagnosis can be made on the hospital floor. If you rotate the vial of pus, the yellow sulfur granules, characteristic of this organism, can be seen with the naked eye.

You can also see these granules by running sterile water over the gauze used to cover the lesion.

The water washes away the purulent material leaving the golden granules on the gauze . This organism, which occurs worldwide, can be seen histologically as "sulfur granules" surrounded by polymorphonuclear cells (PMN) forming the

purulent tissue reaction. The organism is a gram positive rod that frequently branches. The laboratory must specifically be

instructed to culture for this anaerobic organism. These lesions must be surgically drained prior to antibiotic therapy and the drug of choice is large doses of penicillin (2 million

units q 6 h).

GENERA Some facts that you should know about these genera are that: 1- Actinomyces are anaerobic, while Nocardia and Streptomyces are aerobic.

2- Actinomyces produce Sulphur granules. All genera may produce granules. Actinomyces almost always produce granules.

3-Nocardia stain partially acid-fast, Actinomyces and Streptomyces are not acid-fast.